This invention is directed to optical scanning devices, such as bar code scanners, and is more particularly concerned with an arrangement for reading optical symbols, e.g., small linear or two-dimensional bar code symbols that are directly marked on articles. The invention is more particularly concerned with a combination of a hand-held optical scanner and an illuminator that provides stimulating illumination onto a bar code symbol or other symbol which is formed of a fluorescent or phosphorescent or luminescent material. This scanner may be of a corded or cordless variety or built into a data terminal or be of a compact, fixed mount style.
Within the past several years, two-dimensional bar code systems have begun to be employed on small articles so that the article can be tracked throughout manufacturing, packaging, and shipping. In some cases, luminescent or fluorescent bar code symbols are invisibly printed onto articles, e.g., onto the base or bottom of a pharmaceutical vial to identify the contents, as well as to provide information about the batch number, date and place of manufacture. Where 2-D symbols are used, these can carry all the required information within a square that may typically be only three to six millimeters on a side. The symbols can be thermally transferred, screen printed or ink-jet printed directly onto the surface of the pharmaceutical vial or other article. At present, machine-mounted camera-based scanner systems are employed, in which the articles proceed past the scanner station, and the articles receive illumination from a discharge-tube type black light source. These scanner systems are bulky and non-portable, so they cannot be carried by an operator. This makes it impossible to read the bar codes in a warehouse, shipping dock or receiving dock environment where the workers could be provided with hand-held scanners. In addition, because of the rather harmful effects from ultraviolet radiation, conventional black light sources typically have to be shielded to protect the workers from exposure to skin or eyes. Consequently, invisibly printed phosphorescent bar code symbols can only be read under special circumstances, as the bulk, weight, and complexity of the reader equipment has limited their widespread usage.
Recently, short-wavelength light emitting diodes (LEDs) have been introduced. Such LEDs can emit light in the deep blue to near UV region of the spectrum, and can be used to produce black-light illumination. These have been used notably, in combination with an encapsulation of luminescent phosphors, to create so-called white LEDs, in which the short-wavelength light stimulates the phosphors to create a blend of red, green, and blue light. No one previously had considered using black-light emitting diodes in connection with any sort of hand-held scanner device to permit their use in reading “invisible” luminescent or fluorescent optical symbols, such as bar codes.
One previous attempt to incorporate an ultraviolet source into a hand held scanner is discussed in Feng U.S. Pat. No. 6,123,263. That patent deals with a reader that employ discharge tubes or flash tubes with filter elements to cut out some of the UV, so that the emitted light falls in a narrow band of 300 to 400 nm. That device has to strobe continuously, i.e., several times per second, with very high intensity illumination. That patent does not discuss any safety issues, and does not attempt to eliminate or minimize the effects of stray UV illumination.
More recently, the same inventors involved here have produced a scanner which employs black light LEDs for illumination in the blue-violet and near UV region for illuminating bar code symbols that are printed in phosphorescent, luminescent or fluorescent inks. This scanner is described in U.S. Pat. No. 6,824,061, Nov. 30, 2004. The scanner had employed a hollow nosepiece with an opaque shell that concentrates the illumination on the fluorescent target and also helps shield the operator from stray short-wavelength illumination. The nosepiece also keeps ambient light from flooding the imager within the scanner.
Quite recently, fluorescent or luminescent inks have been developed that can be stimulated at visible wavelengths and will produce light at a slightly longer visible wavelength. Other possible inks respond to visible light with fluorescence in the IR region. However, prior hand held scanners are unable to discern bar coded symbols formed of these fluorescent inks, because of the low contrast between the target and background.